The US immigrant population — estimated at 40.4 million in 2011 — is the nation's historical numeric high, and it is also the largest in the world. About 20 percent of all international migrants reside in the United States, even as the country accounts for less than 5 percent of the world's population. Find out more top statistics on immigrants and immigration in the United States in this article which presents the latest, most interesting data in one easy-to-use resource.